Yeast attenuation low/FG too high

lasersnake · Joined: 23 Jan 2018 Posts: 10

Hi Team,

Ever since I have been using my electric brewery (fairly similar to Kals but with 10gal kettles to make 5gal batches but the sensing and heating characteristics are all the same) I have been having attenuation problems and not hitting my FG. There has been 5 batches now.

Previous to this set up I was using a robobrew and never didn't hit an FG, but now I am generally 5 points over on every beer. The fact it is consistent and the only thing that has changed in my process is going from robo to herms makes me very suspicious.

I have been getting yeast attenuation of a couple of percent lower then the minimum usually listed on the packs and I have changed up the methods of pitching (big starters, decanted starter, dry yeast rehydrated & liquid straight from the pouch) in to well aerated wort but still have the consistent 5-6 points above.

All things point towards a mash temp issue, I usually nail my strike water temp and by the time i have stirred the grains in it is sitting at my desired mash temp and doesnt move for the hour i am mashing (maybe takes 2-3mins to stabilise).

I have tested the temp in the mash tun with 3 different thermometers and they read the same as on my PID controllers, but am wondering if there is a problem with it being hotter at the top of the mash tun where the water enters compared to the outlet where the temp is actually controlled off and if I need to adjust my mash temp in my recipes a couple of degrees?

I see a few people have forum posts about this but they always seem to disappear and never post again so wondering if anyone has any advice or experience here?

Any help would be greatly appreciated.

**kal** · Posted: Sun Jul 22, 2018 1:19 pm Post subject:

Can you post some pictures of your setup and more details on the equipment you use?

Do you recirculate your mash pump at max speed (100%) to ensure even temperature? You should not have a noticeable difference in temp between the top and bottom of the mash.

Can you provide an example recipe with all the numbers and details? Including the amount of and type of yeast pitched, and how fermentation was done.

What were the numbers for these 5 batches? All 5 always being 5 points high on FG sounds odd - almost as if there's an issue with how FG is being read maybe? That said, how are you reading FG before on the robobrew and now on the HERMS setup?

Any two systems will have variances in the beer they produce due to differences in the process used. Part of the trick of learning a new setup is learning the process that works on that specific system. The process I use and recommend on this design is here: http://www.theelectricbrewery.com/brew-day-step-by-step
5 points in FG sounds too high to just be a mash temp issue (I find that mash temp doesn't have as huge an effect on FG as the actual recipe does) so I'd be curious to see/read what sort of recipes you're making. How many of these beers were also made on the robobrew? What sort of mash efficiency were you getting on the robobrew? What are you getting now on the HERMS setup? How were the recipes modified to switch from the robobrew to the HERMS setup?

How many batches did you brew on the robobrew?

The more info the better. Right now we unfortunately don't really have anything to go on. It's likely something very simple/straightforward. (It usually always is, like switching to using a different way of measuring FG such as a using a refractometer which can't be used for FG measurements).

Cheers!

Kal

lasersnake · Joined: 23 Jan 2018 Posts: 10

Yeah sorry there was a bit of lack of information.

**kal** · Posted: Sun Jul 22, 2018 11:36 pm Post subject:

Thanks for the info!

Your Stout recipe has 22% unfermentables in it which is really high. To go from 59 to 13 is 77% attenuation, near the midrange for the yeast in question but with 22% unfermentables I think you’re asking for too much.

Kal

lasersnake · Joined: 23 Jan 2018 Posts: 10

**kal** · Posted: Mon Jul 23, 2018 1:00 am Post subject:

Not sure about beersmith, but the brewing software I’ve used doesn’t account for it. Try a simple recipe with all domestic 2-row compared to all crystal something. See what happens.

Software estimates of FG are horribly inaccurate as it’s a really complex thing to try and calculate. Every malt has a different fermentability (it can even vary from batch to batch), every yeast is different, mash temp and thickness affects it, plus dozens of other factors.

Kal

lasersnake · Joined: 23 Jan 2018 Posts: 10

I am pretty confident beersmith does all that for you (after playing with a few recipes and watching the numbers move around).

Here is a better example of recipes I just kegged;

6Foot5 IPA - 23l Batch

6.35kg Pale Malt (93%)
0.16kg Cara-Pils (2.3%)
0.16kg Medium Crystal (2.3%)
0.16kg Vienna (2.3%)

3 Packs of Mangrove Jacks M44 rehydrated. Fermented at 19.5deg for 7 days then slow rise to 21 for 5 days.

Estimated OG = 1.062
Actual OG = 1.061

Estimated FG = 1.011
Actual FG = 1.016

And the other batch;

S Bomb IPA - 23l Batch

6.60kg Pale Malt (89.6%)
0.77kg Medium Crystal (10.4%)

2l Starter with WLP001. Fermented at 19.5deg for 7 days then slow rise to 21 for 5 days.

Estimated OG = 1.066
Actual OG = 1.065

Estimated FG = 1.013
Actual FG = 1.019

It is strange that every batch I do is consistently 5-6 points over on FG, regardless of recipe. The attenuation is 70ish % which is off the lower end of the scale for these yeasts!

**kal** · Posted: Mon Jul 23, 2018 10:01 pm Post subject:

Tungsten · Joined: 06 Dec 2014 Posts: 318 Location: Buffalo, NY

lasersnake · Joined: 23 Jan 2018 Posts: 10

lasersnake · Joined: 23 Jan 2018 Posts: 10

**kal** · Posted: Tue Jul 24, 2018 11:59 pm Post subject:

It’s to know when the entire mash bed is at temperature as that’s what we care about. We already know the temp at the MLT input. That’s the HLT temp. Check out my temp probe and MLT build articles for complete details.

Early on (~10 years ago) I did some tests and the temp at the MLT input always matched what my HLT PID displayed (which makes sense). So no point in measuring there. If the equipment or process is different (ie: using thinner hoses, not recirculating as fast, or something else) then you may get different results.

Kal